The goal of this project is to study the accuracy of optical imaging for the localization of epileptogenic tissue in a primate model of neocortical epilepsy. Approximately 2 million people in the United States have epilepsy, and 20-30% of this population is refractory to all medical treatments. The only viable treatment for patients suffering from intractable epilepsy is surgical resection of the epileptogenic tissue. The surgical outcomes of patients suffering from neocortical epilepsy are only half as good as the surgical outcomes from resections of mesial temporal sclerosis. The main difficulty in the treatment of neocortical epilepsy is that current technology has limited accuracy in mapping neocortical epileptogenic tissue. It is precisely this problem -increasing the accuracy of the localization of epileptogenic tissue in neocortex - that this proposed research aims to solve. To address this problem, we will compare the accuracy of a new optical imaging method to the current clinical 'gold standard' of surface electrode grid array recordings. It is known that the optical spectroscopic properties of brain tissue are correlated with changes in neuronal activity. The method of mapping these activity-evoked optical changes is known as 'imaging of intrinsic optical signals' (IIOS). Activity-evoked optical changes measured in neocortex are most likely generated by changes in cerebral hemodynamics (i.e. changes in blood oxygenation and blood volume). Our experimental approach will be to acquire high resolution IIOS maps of epileptiform activity in an acute primate model of epilepsy, and to carefully compare the accuracy of IIOS maps to the current 'gold standard' -- recordings from surface electrode arrays. Our specific aims are to i) Determine the accuracy of optical spectroscopy for localizing neocortical neuronal populations involved in the generation and spread epileptogenic activity, and ii) Compare the accuracy of optical spectroscopic mapping to the 'gold standard' electrode grid arrays to guide the surgical resection of epileptic tissue.